What is an MQL lubrication system?

A Minimum Quantity Lubrication system delivers MQL fluid to the cutting tool/workpiece interface. The most common way this is accomplished is by propelling the lubricant to the target with an air atomized spray. The lubrication system allows users to precisely control the flow rate of lubricant and air to dial-in the amount of lubricant for the process. The fine droplets of oil are carried by the compressed air stream to the cutting surface where they lubricate the cutting process.

Flow rate adjustability is critical as each operation could require a different amount depending on the tool, the material, the speed, and the depth of the cut. The lubrication system should be easily adjustable and responsive to changes by the operator. For automated processes, the ability to save and recall settings is important to maximize the consistency of the lubrication process. The goal is adjustable and repeatable delivery of the lubricant.

What are the elements of a lubrication application system for metal cutting & machining?

What is a positive displacement lubrication pump?

In manufacturing operations, consistency is key. Positive displacement pumps are just that - consistent. The volumetric output of the pump per stroke is consistent regardless of ambient temperature, output pressure, fluid viscosity, and any other external variables. The pump itself can be thought of like a syringe where the piston moves into the pump chamber and positively displaces the fluid that was there. This is different from many types of lubrication pumps.

A positive displacement pump is at the heart of all Unist MQL systems. Positive displacement ensures that the same volume of lubricant is dispensed with each pump cycle, improving the function of the lubrication system. Simply adjust the rate at which the pump cycles, and the amount of fluid delivered to the process easily be adjusted.

positive displacementPositive Displacement
An easy way to understand the concept of positive displacement is to think of a syringe. When the syringe's plunger is pulled back, a known volume of fluid is drawn into a cavity. This known volume of fluid is dispensed when the plunger moves forward and displaces it. This is the same concept found in an MQL system's pumps and provides the advantage of being able to control the lubricant quantity dispensed.

Unist has several pump options available. When selecting a pump, users must first consider the viscosity of the fluid they wish to dispense. Unist offers standard pumps to handle viscosities between 50 and 1000 SUS and also a multi-viscosity ("MV") pump which can handle an expanded viscosity range of between 30 and 1300 SUS. The second consideration is the desired volumetric output of the pump. Consult the list below to determine which pump is required based on output and fluid viscosity.

Available Unist pumps:

Standard 1-drop pump
Standard 1-drop pump
(0.03 mL per stroke): 50-1000 SUS
Standard 3-drop pump
Standard 3-drop pump
(0.10 mL per stroke): 50-1000 SUS
Multi-Viscosity 1-drop pump
Multi-Viscosity 1-drop pump
(0.045 mL per stroke) : 30-1300 SUS
Multi-Viscosity 2-drop pump
Multi-Viscosity 2-drop pump
(0.10 mL per stroke) : 30-500 SUS

1-line vs. 2-line lubrication systems

Single line, or 1-line, lubrication systems mix the air and the lubricant right at the applicator and carry the atomized mixture through tubing to the point of application. Dual-line, or 2-line, systems keep the air and oil separate as far as possible, mixing at the point of application (nozzle tip). Typically, the best way to ensure a consistent and responsive atomized spray is to keep the fluid and air separate until you're ready to apply it.

One way this is accomplished is by using coaxial tubing (a tube within a tube) which keeps air and oil separated from each other until the nozzle. This allows the best response time when turning outputs on or off or when adjusting the mixture of fluid and air even over long tubing runs. A single line lubrication system can be used when the tubing runs are short and the need for rapid on-off or rate adjustments is not present, including for single line progressive lubrication systems. There are many different methods of applying cutting fluids in machining processes.

What types of nozzles are available for MQL systems?

The nozzle is the last component before the point of application and controls the spray pattern's shape and size. The nozzle is a critical part of the whole system because even the most precise applicator is useless if not aimed correctly at the target. There are several styles of MQL nozzles available depending on the operation.

Most commonly, nozzles are external, meaning that they mount beside the cutting tool in some fashion and spray onto the cutting tool. Several types of nozzles are available to suit many applications from flexible plastic or semi-rigid copper, to stainless steel nozzles. Also available are magnetic and articulated arm mounting options.

Sawing operations often have unique nozzles tailored for the type of saw blade. On circular saws, a special three-outlet nozzle is commonly used to evenly coat the sides, teeth, and gullet of the saw blade. Band saw nozzles are shaped like a “U” and apply the lubricant to the teeth of the blade. Also, MQL can be used to finely coat the sides of a band saw blade to lubricate carbide blade guides.

Sometimes MQL can be routed through the machine to the point of application, for example, in the case of a mill or lathe. In a mill or milling machine lubrication system, some might choose to implement through-spindle MQL. This means that the MQL travels through the rotating spindle and exits through channels in the cutting tools. This provides the most targeted application as the lubricant exits right at the cutting edge of the tools, however, it is more difficult to implement when compared to external nozzles.

On a lathe, the atomized MQL could be routed through the turret through existing flood coolant passages. Each tool station on the turret would be equipped with a nozzle specific for that cutting tool. This provides excellent coverage of each cutting tool as each has its own dedicated nozzle in the lubing system specifically tailored to aim the lubricant where it needs to be.

Minimum Quantity Lubrication System Setup and Maintenance

The setup and maintenance of an MQL application system are simple. Typically all that is involved is mounting the system, filling the reservoir, aiming the nozzles, and turning the system on. The most involved part of the MQL setup is determining the correct settings for air and oil flow. Sometimes users get too much mist. In this case, the pump may be running too fast and they are getting too much oil. Sometimes excess mist is caused when the airflow is turned up too high, causing excessive fogging of the fluid.

Each of these situations is easily fixed with adjustments. We can provide suggestions for nozzle placement or whether you’ll need a single or multi-nozzle setup, suggest setups for progressive systems, as well as baseline starting points for various system settings.

As long as clean fluid is put into the system, maintenance needs are minimal. If the reservoir runs dry, the pumps may need to be primed. Some Items within the system could wear down over years of use, but if our pumps are used exclusively with Coolube fluids, we guarantee the pump for life. Changing or rebuilding a pump out only takes a few minutes and you’ll be back up running very quickly with minimal downtime.